Chemical sensors and biosensors in the form of volume holograms made in specially made polymer layers are known. WO-A-95/26499 discloses a sensor which comprises a reflection hologram made in a thin film of polymeric material where the polymer interacts with a substance to be detected so as to alter the optical properties of the hologram, thereby providing a means for detecting or quantifying that substance. More generally, this reference and also WO-A-99/64308 disclose the concept of a volume hologram sensor which provides a measurable or observable optical change.
Within the art of holography, multiple holographic images and methods for creating them in a single holographic recording material are known. U.S. Pat. No. 4,509,818 discloses a method of making a three-dimensional holographic multiplexed image from a series of two-dimensional images. U.S. Pat. No. 5,103,325 discloses a method of holographically recording a series of two-dimensional images such that the viewed holographic images are observed separately and distinctly from each other. U.S. Pat. No. 5,734,485 discloses a method of producing three-dimensional still or moving scene holograms including recordings of computer-generated scenes.
These known systems produce sets of holographic images which are multiplexed in a degree-of-freedom which is only spatial, where the images are intended to be viewable by an observer as an artificially-produced three-dimensional image or as a set of images separated in space over a corresponding set of angles of view. The optical properties of the material in which these holograms are made are intended to be invariant in time and they are not intended to be altered chemically when functioning normally.